Mercury/Yamaha 4 cylinder

I picked up a 1987 Sylvan with a 4 cylinder I/O. The rocker cover and name plate say Mercury and Yamaha is cast into part of the exhaust system.

The nameplate gives a serial number (L659xxx) but I can't find a model number anywhere.

I would like to find out more about this engine. Does anybody know of an online source for data on Mercury/Yamaha.

Thanks

 

pictures pictures pictures ....

 

Yamaha briefly entered the stern drive market with their own drive and the same GM 4-cyl. engine used by Mercruiser for the 120-140 hp packages.

The drive resembles an Alpha-1 but differs in every detail, so you can only replace items with genuine Yamaha parts. They are still available but painfully expensive.
The drive had a good resistance to corrosion but was not as mechanically strong as it should have been. Too much torque on the lower-to-upper housing bolts could result in cracks and oil leaks.

On the Yamaha outboards website you'll find diagrams, drawings and parts lists.

 

The drive has a clutch dog that is what usually wears. Yamaha had a lot of complicated electronics and sensors. Most of the time, I have replaced the whole electronics with a Mercruiser which also has the shift interupt switch

 

I found my engine/stern-drive model - it was on the back of the stern-drive. It is an "L4 3.0" rated 130 HP. Ought to be a zippy little boat

 

For about 3 years Yamaha made sterndrives using 3.0, 5.0. 5.7 and 7.4L engines. The metallurgy in them was superb, but a court case from Mercruiser pulled them off the market.
parts are available down here in the land of Oz and several places in Europe advertise parts over there, so you should be able to keep it going for some time.
If your rocker cover says Mercury, I'd say it has been changed at some stage, as Yamaha made almost all there own badged parts.
My 5.7L Yamaha has Mercruiser manifolds and risers but they needed a couple of slight modifications to suit - no major surgery just a bit of a fiddle to fit.
If you are getting it serviced, make sure to tell the mechanic that to remove the leg the gear must be in Neutral, not forward as with Mercruiser, or they/you will break the shift fork.